Color photographic light-sensitive materials generally comprise at least two silver halide emulsions having each a different color sensitive property (the term "color sensitive property" means the property of being sensitive to any light of three regions in the visible spectrum, namely, red, green and blue) on a base, wherein each layer contains a silver halide emulsion and a dye forming coupler, namely, a compound capable of coloring in color development processing by coupling with an oxidation product of an aromatic primary amine developing agent (for example, phenylenediamine derivatives or aminophenol derivatives, etc.).
Sometimes, photographic light-sensitive materials are used under conditions of very low exposure amount. For example, there is the condition of taking a photograph of athletic sports which requires a high shutter speed or a photograph of the stage in a dark theater. In the case of taking such photographs, photographic light-sensitive materials having high sensitivity are required, and a high sensitization of light-sensitive materials and an increase of sensitivity by processing are carried out. The increase of sensitivity by processing is called, generally, "sensitization processing," which is carried out by changing the composition of the developing solution for standard processing, raising the development temperature or prolonging the development time.
However, the prior photographic light-sensitive materials do not always have sufficient sensitization processing aptitude, and also have the following problems:
(1) in the case of carrying out sensitization processing, the degree of increase of sensitivity from that of standard processing (hereinafter referred to as "width of sensitization") is insufficient, PA1 (2) in light-sensitive materials in which the emulsion layer is divided into a high speed layer and a low speed layer each of which has the same color sensitivity, tone (gradation) is different from that obtained by standard processing when the layers are subjected to sensitization processing, because the width of sensitization is different in both layers, or PA1 (3) particularly, in color light-sensitive materials, when they are subjected to sensitization processing, deterioration of color balance occurs, because the widths of sensitization of the red-sensitive layer, the green-sensitive layer and the blue-sensitive layer are different from one another.
Therefore, in order to improve the sensitization processing aptitude of, particularly, color photographic light-sensitive materials, it is necessary to develop silver halide photographic emulsions having a sufficiently large width of sensitization and to develop an art of exactly controlling the width of sensitization over a wide range.
The present invention has been developed to meet such technical requirements, and an object of the present invention is to provide color photographic light-sensitive materials having improved sensitization processing aptitude and to provide an art of controlling the width of sensitization arbitrarily in a wide range.
In order to control the width of sensitization arbitrarily, it is necessary to have a means for expanding the width and a means for reducing the width. Sensitization wavelengths of silver halide range up to blue light, and a spectral sensitization technique using the so-called sensitizing dyes is well known in the field of the art as a means of expanding sensitivity to a longer wavelength range. As a result of studies by the present inventors, it has been found that the sensitizing dye not only shows spectrum sensitization but also has a large influence upon sensitization processing aptitude. Namely, in a silver halide emulsion using a certain kind of sensitizing dye, the width of sensitization in the case of sensitization processing is large and, in a silver halide emulsion using another kind of sensitizing dye, the width of sensitization is small. Therefore, it has been expected that the width of sensitization in silver halide emulsions sensitized with the former sensitizing dyes can be controlled arbitrarily over a wide range, if combined with a substance which suppressively serves for development. However, the substance which suppressively serves for development is that which is effective only in the case of sensitization processing, and it is preferred that the substance does not show an inhibiting action in the case of standard processing. Namely, it is necessary that the substance acts to reduce the width of sensitization by use with a sensitizing dye but does not greatly reduce photographic sensitivity in standard processing or does not greatly change gradation. Thus, it is very difficult to find such a substance.